roles/certbot: Run periodically as certbot user

The default systemd unit configuration for *certbot-renew.service* runs
the `certbot renew …` command as root. This can cause permissions
issues, since this Ansible role expects the *certbot* user to be able to
access all configuration, data, and log files. As such, this commit adds
a systemd unit extension for *certbot-renew.service* to run the command
as *certbot*.

roles/certbot/files/certbot-renew-runas.service

@@ -0,0 +1,3 @@
+[Service]
+User=certbot
+Group=certbot

roles/certbot/handlers/main.yml

@@ -1,3 +1,5 @@
+- name: reload systemd
+  command: systemctl daemon-reload
 - name: reload httpd
   service:
     name=httpd

roles/certbot/tasks/main.yml

@@ -92,6 +92,17 @@
     dest=/etc/sysconfig/certbot
     mode=0644
 
+- name: ensure certbot renew service extension directory exists
+  file:
+    path=/etc/systemd/system/certbot-renew.service.d
+    mode=0755
+    state=directory
+- name: ensure certbot renew runs as certbot user
+  copy:
+    src=certbot-renew-runas.service
+    dest=/etc/systemd/system/certbot-renew.service.d/run-as-certbot.conf
+    mode=0644
+  notify: reload systemd
 - name: ensure certbot timer is enabled
   service:
     name=certbot-renew.timer